1. Field of the Invention
This invention relates to a magnetic recording medium and to a method for its preparation, and is particularly directed to an improved method for dispersing magnetic powder into a resinous binder to achieve improved residual magnetic flux density B.sub.r, improved squarness ratio R.sub.s, and a better packing density.
2. Description of the Prior Art
In the manufacture of magnetic recording media, magnetic powder is treated by means of various kinds of dispersants or surfactants in order to improve the dispersion of the magnetic powder in the magnetic coating material. Surfactants such as fatty acids, metallic salts of fatty acids (metallic soaps) or the like have been used. However, when these materials are used in a magnetic medium, their surface activity is not sufficient and therefore do not improve the dispersion greatly.
In other examples of the prior art, there has been proposed a method in which the magnetic powder is treated preliminarily by lecithin. In this proposal, however, ordinary lecithin as available on the market was used, this being a raw lecithin which includes a large quantity of impurities.
There has also been proposed a method by N. Kazino et al. in Japanese Laid Open Specification No. 309/1976, a method which uses a lecithin prepared in such a manner that ordinary lecithin is extracted with acetone to remove neutral fats or fatty acids. Even with the acetone extracted lecithin, however, the degree of dispersion of magnetic powder achieved is insufficient.